1. Field of the Invention
The present invention relates to an electronic weighing scale using a general purpose block member which can be utilized as a Roberval mechanism or as an elastic body of an electronic weighing scale of a load cell type, and more particularly to an electronic weighing scale of an electromagnetic equilibrium type using the general purpose block member as an integral type Roberval mechanism.
2. Prior Art
The electronic weighing scale of the electromagnetic equilibrium type which is referred to as an electronic balance comprises a load receiving portion for receiving the load of an object such as a weighing scale pan, an electromagnetic portion for generating electromagnetic force which equilibrates with the load, a load transmitting mechanism for transmitting the load received by the load receiving portion to the electromagnetic portion, and a Roberval mechanism for guiding the load transmitting mechanism.
These mechanisms are constituted by assembling several tens of parts, for example, various members such as a load transmitting beam, a member for constituting the Roberval mechanism, a connecting member such as a leaf spring for connecting these members, a screw for fixing these members and the like.
As a matter of course, with the above-mentioned structure, an assembly man-hour is great and it is necessary to finely adjust each portion of the mechanism with complexity after the assembly as a result of the combination of a large number of parts. If the mechanisms are formed of one material and are changed into one block, the assembly man-hour can be reduced greatly.
In consideration of this respect, there has been proposed an electronic balance using a block member of a complete integral type which constitutes each portion except the electromagnetic portion as one metal block. The block of the complete integral type is obtained by forming originally individual members from one metal block. Therefore the internal shape of the whole block is complicated and a high working precision is required.
An example of the block has been disclosed in U.S. Pat. Nos. 4,799,561 and 5,525,762, German Patent Nos. DE19754172C1 and DE19540782C1 and the like. Since these have a structure in which an electromagnetic portion for generating equilibrium force is housed in a block, mechanisms can be constituted to have small sizes but their shapes are very complicated.
U.S. Pat. No. 5,315,073 (EPC Patent No. EP055876B1) has disclosed a structure in which an electromagnetic portion is arranged in the concave portion of a block having one of ends opened. In this respect, the structure is slightly simpler than the block structure. However, the fulcrum of a lever for transmitting a load is elastically supported. Therefore, a high working precision is required.
As described above, although the main parts of an internal mechanism constituting the electronic balance is formed into one block to obtain great advantages, the following problems arise and the solution of the problems has been desired.
First of all, as the premise of the formation into one block, an almost rectangular metal block such as an aluminum based alloy is subjected to a fine working. Thus, a load receiving portion, a load transmitting portion using a lever, a thin deforming portion for permitting the operation of the load transmitting portion, a Roberval portion for guiding the load transmitting mechanism, a thin fulcrum portion and the like are formed for the metal block. The one-block working is carried out by performing the complicated and fine cutting for the metal block using means capable of performing a fine working such as cutting working, a discharge machining device using wire cutting as described in U.S. Pat. No. 5,340,951. For this reason, a high working precision is required over the whole metal block and a special working method is necessary. Therefore, the productivity of the block is not always high.
In the electronic balance in the working stage or thus manufactured, even if troubles are made on a part of the block, the problematic parts cannot be exchanged because of the integral properties. Therefore, there is a problem in that the whole block cannot be used. Any structure of the block is basically formed by working the almost rectangular metal block. For this reason, portions to be operated as respective members are arranged in the rectangle as a matter of course. Also in this respect, the arrangement of the portions to be the respective members has a restriction. For example, there is a problem in that a high leverage cannot be taken including the problem of the strength of the block in a member for transmitting a load, for example. Moreover, with such a structure as to form each member in a block member by a fine space obtained by a wire cutting discharge machining, the width of the cut space is very small, for example, approximately 0.3 mm. Therefore, refuse gets into the space portion, thereby causing an operation failure.
Also in a normal block member, it is always necessary to perform an adjusting work for the whole weighing scale mechanism when constituting the weighing scale mechanism by the assembly of the block member to the device and the fixation of the member such as the weighing scale or the like to the block member. This respect will be described by using a block model having a simplified structure with reference to FIG. 17.
An integral type Roberval mechanism 420 formed integrally with a metal block such as an aluminum member has elliptical space portions 422A and 422B formed on both ends through a central communicating space portion 421. Consequently, thin portions 422Aa, 422Ab, 422Ba and 422Bb are formed on the upper and lower portions of the space portions 422A and 422B, respectively.
In the integral type Roberval mechanism 420, fine adjustment is carried out by scraping any of the thin portions of the integral type Roberval mechanism 420 by means of a file or the like to make the same portion thinner corresponding to a shift error. More specifically, the fine adjustment is carried out by diagonally cutting any of front portions 422Aa1, 422Aa2, 422Ba1 and 422Ba2 of the upper thin portion 422Aa. In addition, it is necessary to adjust the thickness of the whole thin portions 22A and 22B when adjusting the error of the front and rear relationship of the shift error. Forth is reason, the adjusting work cannot be easily carried out even in the integral type Roberval mechanism 420 having a simple model as shown. Furthermore, it is very hard to carry out the adjusting work for a complicated block member of the integral type.
In consideration of such a request, it is an object of the present invention to provide an electronic weighing scale which removes the problems of a complete integral type block member and has a small-sized mechanism portion capable of saving parts, an electronic weighing scale using a general purpose block member of an integral type which is constituted to be operated as a Roberval mechanism or an elastic body of a load cell corresponding to an electronic weighing scale of an electromagnetic equilibrium type or an electronic weighing scale of a load cell type, and an electronic weighing scale constituted to simplify a block structure more than a complete integral type block member, to easily execute the adjustment of the block member and to carry out application of a load to the block member more properly.
A first structure of the present invention is directed to an electronic weighing scale using an integral type block member constituted to operate as a Roberval mechanism or an elastic body of a load cell, the integrally formed block member including a load receiving portion for receiving a load of a scaled object, a fixing portion for fixing the whole block, and a Roberval portion formed as a space portion having a thinned portion between the load receiving portion and the fixing portion for operating as a Roberval, wherein a member for transmitting a displacement of a load transmitting beam and the load receiving portion to the load transmitting beam and for becoming a force point of the load transmitting beam and a member to be a fulcrum of the load transmitting beam are formed separately from the block member, and a member attachment portion constituting a fulcrum and a force point is formed on the block member such that the fulcrum or force point of the load transmitting beam is positioned in a space or closely to the space, preferably, the member to be the fulcrum is positioned on right and left sides of the Roberval portion, thereby constituting the electronic weighing scale of an electromagnetic equilibrium type.
A second structure of the present invention is directed to an electronic weighing scale using an integral type block member constituted to operate as a Roberval mechanism or an elastic body of a load cell, the integrally formed general purpose block member is provided with a space portion having a thinned portion in four upper and lower portions between a load receiving portion for receiving a load of a scaled object and a whole block, a working guide portion indicating a part to be thinned by cutting or the like is formed on at least one of surfaces of the thinned portions in two upper places, and an adjusting portion for performing adjustment by thinning a predetermined part of the working guide portion from above the Roberval portion is provided.
A third structure of the present invention is directed to an electronic weighing scale using an integral type block member constituted to operate as a Roberval mechanism or an elastic body of a load cell, wherein a support member for supporting the general purpose block member includes an attachment portion fixed to a side edge of the general purpose block member and a fixed portion for horizontally supporting the general purpose block member which is attached to the attachment portion, a load transmitting member for transmitting a load to the general purpose block member has an attachment portion to be attached to a block side edge on a side opposite to the side edge on the support member attachment side, and a load receiving portion positioned in parallel with a body portion of the support member through a block, a member for directly receiving a load such as a weighing scale pan is connected to the load receiving portion of the load transmitting member, and the support member and the load transmitting member are formed almost point symmetrically with each other by using, as a symmetrical point, a point positioned in almost a central portion of the general purpose block member, and an applied load and reactive force to the load are positioned on almost the same axis.